DE10243983B4 - Method and device for the early detection of a generator defect - Google Patents

Abstract

A method for the early detection of a generator defect in a generator (1) with a generator controller (4) for setting the generator output power, the generator controller (4) controlling a switch (6) arranged in an excitation circuit (7) with a predetermined pulse duty factor (DF), characterized by the following steps: - Determining the duty cycle (DF); Determination of the excitation current (Ierr) flowing in the excitation circuit (7) - Detecting a generator failure on the basis of the duty cycle (DF) and the excitation current (Ierr); a generator defect is detected when the excitation current for a given pulse duty factor (DF) is outside a tolerable range - and this detection is done by means of threshold monitoring, the threshold values for the excitation current or the pulse duty factor or a ratio formed from these values are stored in the system.

Description

The invention relates to a method for the early detection of a generator defect on a generator with excitation circuit according to the preamble of patent claim 1, and to a corresponding device for detecting a generator defect according to the preamble of patent claim 7.

An early detection of a generator defect is particularly important when safety-related devices are connected to the generator, which may be affected by a possible generator failure. Especially in motor vehicle electrical systems, in which usually a variety of safety-related facilities, such. As vehicle dynamics control systems, ASR systems or other safety-related controls are connected, can result from a generator failure, but even by a generator underpower due to a generator defect, a significant security risk.

It is already known to detect generator errors by threshold monitoring of the mains voltage (voltage of the network supplied by the generator). However, it is only possible serious generator defects and in particular the total failure of the generator, eg. B. due to an electrical interruption or a short circuit in the runner, determine. In these cases, the mains voltage drops drastically and falls below predetermined threshold values, whereby a generator defect can be detected.

Not recognized, however, are less serious generator defects, such. B. partial short circuits or increased resistances in the exciter circuit of the generator, which also lead to a reduced power, but which does not affect so much that the mentioned threshold values for the mains voltage are exceeded. However, these less serious errors are the first signs of a possible later failure of the generator. So far, it is not yet possible to detect such generator errors.

From the DE 40 37 640 A1 For example, a voltage regulator for a generator is known in which a switching transistor is used to control the excitation current. The switching transistor is controlled by means of a clocked signal, wherein the duty cycle of the drive signal is decisive for the exciter current.

From the DE 196 23 808 A1 a device is known which makes it possible to monitor the excitation current, the excitation voltage and a possible ground fault of the rotor winding of an electrodynamic machine during operation.

The DE 37 30 829 A1 relates to an overload protection for the excitation circuit of a synchronous machine, in which the excitation current is determined from measured variables and an overload protection is activated when a permissible maximum value is exceeded.

From the DE 29 26 705 A1 a circuit for detecting defects in vehicle on-board networks is known in which defects of the exciter circuit of an alternator contained in the electrical system are displayed optically. In particular, serious errors such as over or under excitation of the alternator are displayed.

It is therefore the object of the invention to provide a method and a device with which such less serious generator defects can be detected.

This object is achieved according to the invention by the features specified in claim 1 and in claim 7. Further embodiments of the invention are the subject of dependent claims.

The essential idea of the invention is to determine the exciting current flowing in the field circuit of the generator as well as the associated pulse duty factor with which a switch (output stage transistor) arranged in the excitation circuit is driven. Based on the duty cycle and excitation current, a generator defect can be detected even before the generator completely fails.

With a functioning generator, the excitation current is always in a predetermined ratio to the current duty cycle. If this ratio shifts, this indicates a generator defect.

A partial short circuit between several windings of the excitation circuit, for example, changes the total resistance of the exciter circuit and thus has an effect on the exciting current flowing in the excitation circuit. Similarly, a change in the contact resistance (eg, by corrosion) between a carbon brush and a slip ring of a generator with excitation winding in the rotor, such. As a Klauenpolgenerator, a change in the total resistance of the exciter circuit and thus a change in the exciting circuit flowing excitation current result. The excitation current, which can change due to different mechanical effects or aging phenomena, thus provides information about the generator state.

If, at a given pulse duty factor, an excitation current that is outside a still tolerated range is present, it is possible to conclude that there is a generator defect. This detection is usually done by threshold monitoring.

The corresponding thresholds, e.g. B. for the excitation current, the duty cycle or a ratio formed from these two values are preferably stored in the system.

According to a preferred embodiment of the invention, a ratio of the current excitation current and the current duty cycle is formed and compared with predetermined threshold values.

In the determination of the generator state, further factors which influence the excitation current are preferably taken into account. This makes it easier to differentiate external influences from internal defects.

One of these influences is the temperature and in particular the generator temperature, which has an influence on the total resistance of the exciter circuit and thus on the exciter current. The threshold values stored in the system are thus preferably also a function of the temperature.

Furthermore, the excitation voltage applied to the excitation circuit is preferably taken into account, since the excitation voltage likewise influences the excitation current.

In addition to this electrical monitoring, the mechanical state of the generator, in particular the condition of the generator bearings, can also be monitored. This can be z. B. by a noise measurement with threshold monitoring or by vibration or acceleration measurement. If, for example, abnormal vibrations occur in a certain speed range of the generator, this can be detected by an acceleration sensor and a mechanical generator defect can be determined.

Upon detection of a generator defect, a generator error message is preferably output, for example by visual or audible indication. In the case of a vehicle electrical system generator, for example, an entry in an electronic list of defects can be made. Depending on the severity of the defect, different entries are conceivable.

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

1 a schematic view of a vehicle electrical system with a generator and a generator controller; and

2 a flow chart illustrating the main steps of the invention.

1 shows a schematic representation of a vehicle electrical system with multiple electrical loads, of which only one consumer 2 is shown as an example. For switching the consumers on and off 2 in each case a switch S is provided.

The consumers 2 be from a generator 1 and a battery 3 supplied with electrical energy.

At the generator 1 it is usually a Klauenpolgenerator with an arranged in the rotor exciter winding 5 , The generator 1 further includes a generator controller 4 for setting the generator output power.

The generator controller 4 this includes one in the exciter circuit 7 of the generator 1 arranged switch 6 (Endstufentransistor), which depends on the electrical load of the generator 1 is switched on and off with a predetermined duty cycle. In this case, an excitation current Ierr sets in, the duty cycle (DF signal), the total resistance of the exciter circuit 7 and an excitation voltage Uerr is dependent.

During the life of the generator 1 different mechanical or electrical defects in the generator, such. Partial shorts, increased resistance between coal and slip ring of the generator 1 , as well as aging phenomena, such. As corrosion, occur, which is the total resistance of the exciter circuit 7 change. With the same excitation voltage Uerr and predetermined duty cycle, the excitation current Ierr thus also changes. Generator defects in which the generator 1 Although still functional, but only generates a power underrun, can thus be recognized taking into account the duty ratio DF and the excitation current Ierr.

For early detection of such generator defects is a device 8th provided by a measuring device 9 measured excitation current and the DF signal is supplied. The unit 8th can detect from the two quantities supplied by threshold monitoring a generator defect and initiate appropriate action.

To determine a generator defect, the unit forms 8th Preferably, a ratio of the excitation current Ierr and the duty cycle DF and compares this ratio with predetermined threshold values. If the ratio is within a tolerance range between two thresholds, then the generator is 1 fully functional. On the other hand, if the ratio exceeds or falls below one of the predetermined limits, it can be assumed that there is a generator defect.

The thresholds are z. B. also in the device 8th deposited.

Since the total resistance of the exciter circuit 7 and therefore also the excitation current Ierr is dependent not only on internal defects but also on external influencing variables, preferably also such external influencing variables, such as eg. B. the temperature or the excitation voltage Uerr considered in the error detection.

In this case, the device will 8th the appropriate sizes, z. As the temperature or the excitation voltage, also supplied to take these into account. In this case, the threshold values are a function of the temperature and / or the excitation voltage Uerr.

Upon detection of a generator failure, the unit may 8th For example, cause the output of an optical or acoustic signal indicative of the corresponding error. Alternatively, an entry in a list of defects can be made, which is read out at the next car service.

2 again shows the essential process steps in the early detection of a generator defect.

This is in step 10 First, the current duty cycle (DF signal) is determined and in step 11 the exciter current Ierr measured by the ammeter is read. From these two values becomes in step 12 a ratio V formed in step 13 is compared with predetermined thresholds SW. In this way, it can be determined whether the exciting current Ierr flowing at the current duty ratio DF is within the tolerance range limited by the threshold values SW. Returns the query in step 13 in that the ratio V is within the tolerance range (J), the procedure is finished. By contrast, if the ratio is outside the tolerance range (N), then in step 14 an error message is issued. This can be z. B. in the form of optical or acoustic signals.

LIST OF REFERENCE NUMBERS

1

generator

2

consumer

3

battery

4

regulator

5

excitation winding

6

amplifier switch

7

excitation circuit

8th

processing unit

9

ammeter

10-14

steps

ierr

excitation current

Uerr

excitation voltage

DF

clock signal

U _N

mains voltage

S

switch

Claims (7)

Method for the early detection of a generator defect on a generator ( 1 ) with generator controller ( 4 ) for adjusting the generator output power, wherein the generator controller ( 4 ) one in an exciter circuit ( 7 ) arranged switches ( 6 ) with a predetermined duty cycle (DF), characterized by the following steps: - determining the duty cycle (DF), - determining the in the exciter circuit ( 7 ) detecting a generator defect based on the duty ratio (DF) and the exciting current (Ierr), wherein a generator defect is detected when the exciting current at a given duty ratio (DF) is outside a tolerable range, and this detection By means of threshold value monitoring, the threshold values for the exciter current or the duty ratio or a ratio formed from these values are stored in the system. A method according to claim 1, characterized in that for detecting a generator defect, a ratio of the excitation current (Ierr) and the duty cycle (DF) is formed and this ratio is monitored by means of threshold monitoring, whether it is outside a predetermined range. A method according to claim 1 or 2, characterized in that factors are taken into account for detecting a generator defect, which in the exciter circuit ( 7 ) influence flowing excitation current (Ierr). A method according to claim 3, characterized in that the factors taken into account for the detection of a generator defect is a temperature, in particular the generator temperature. A method according to claim 3, characterized in that in addition to the detection of a generator defect, the excitation voltage (Uerr) is taken into account. Method according to one of the preceding claims, characterized in that further the condition of a generator bearing is taken into account. Device for the early detection of a generator defect on a generator ( 1 ) with generator controller ( 4 ) for adjusting the generator output power, wherein the generator controller ( 4 ) one in an exciter circuit ( 7 ) arranged switches ( 6 ) with a predetermined duty cycle (DF), characterized by a unit ( 8th ) for detecting a generator defect to which the exciting current (Ierr) and the duty ratio (DF) are supplied, and which determines the generator defect based on the duty ratio (DF) and the exciting current (Ierr) by a ratio of the exciting current and the duty ratio is formed and this is compared with predetermined thresholds.

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